This invention relates to a chemical vapor deposition apparatus, especially suitable for application to a metal organic chemical vapor deposition (MOCVD) apparatus.
Devices manufactured by using III-V compound semiconductors, such as light emitting devices including LEDs and semiconductor lasers, and other devices like communication-purpose high-frequency transistors, are important devices constituting hardware infrastructures of the modern communication society, together with silicon (Si)-based devices.
III-V compound semiconductor devices, having structures ingeniously making use of hetero junctions of III-V compound semiconductors, take a complementary part with Si-based devices in regions impossible to realize with Si.
For manufacturing compound semiconductor devices including III-V compound semiconductors, excluding simple-structured devices such as MESFET, hetero epitaxial techniques are important techniques. It is no exaggeration to say that hetero epitaxial techniques basically support the manufacture of such devices. Molecular beam epitaxy and chemical vapor deposition, in particular MOCVD, are currently major hetero epitaxial techniques, which have been studied in laboratories since 1960s.
MOCVD was bought into practice as an epitaxial growth technique for manufacturing GaAs semiconductor lasers. Currently, an MOCVD apparatus enabling epitaxial growth on a number of substrates simultaneously is commercially available. In terms of componential techniques of the multi-substrate MOCVD apparatus, there are various types. Regarding the susceptor configuration, there are a barrel type and a pancake type. In terms of the gas flow mode, there are a high-flow-rate horizontal type, high-revolution type, vertical down-flow type, and so on. In terms of the substrate-supporting mode, there are schemes of putting substrates above the gas flow (face-down) or putting substrates under the gas flow (face-up). Regarding heating there are a RF induction heating type, electrical resistance heating type, lamp heating type, and so on. These componential techniques are combined variously to make up various types of MOCVD apparatuses.
Conventional MOCVD apparatuses for epitaxial growth of III-V compound semiconductors uses gallium (Ga), aluminum (Al) or indium (In) as a group III element and arsenic (As) or phosphorus (P) as a group V element, and the growth temperature was 800° C. at most. On the other hand, there is a recent demand for an MOCVD apparatus capable of epitaxially growing GaN compound semiconductors using ammonia (NH3) as a source material.
A MOCVD apparatus for GaN semiconductors is configured to invite reaction of a group III organic metal compound and ammonia (NH3) at a temperature around 1100° C. to grow a single-crystal thin film on a sapphire or SiC substrate. Concerning the single-crystal thin film, gas composition and growth conditions for growing high quality crystals were academically reported and known. However, MOCVD apparatuses for realizing optimized gas composition and growth conditions for obtaining high quality crystals have been modified after individual technical researches, and almost none of their actual improvements are known. Among some known MOCVD apparatuses, there are some proposals directed to the structure of the reaction tube (for example, Japanese Patent Laid-open Publications Nos. JP-H02-288665A, JP-H04-94719 A and JP-H11-12085). Even with these techniques, it has been difficult to manufacture semiconductors of long-lasting good crystal qualities under acceptable reproducibility because of various entangled factors.